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Four young children in two provinces have been identified with paralysis caused by polio infection

The World Health Organization is boosting monitoring, testing and immunization efforts

(CNN)Two separate outbreaks of polio have been reported in remote parts of the Democratic Republic of Congo, a setback for large-scale efforts to eradicate the highly infectious and potentially fatal disease.

There is a high risk of the disease spreading across the country, though not beyond its borders, the World Health Organization (WHO) warned Tuesday in a statement.

Four cases have been reported in children between 17 and 36 months old in the provinces of Haut Lomami and Maniema, both in the center of the country.

All four children are paralyzed and are being monitored, the WHO said. Their families also are being monitored and getting tested regularly to see if they become infected.

"This is not unusual; it is usually the very young who are most at risk," said Oliver Rosenbauer, WHO Global Polio Eradication Initiative spokesman. "It further underscores the risk, how quickly polio can re-emerge in polio-free areas."

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One type of the virus was found in two cases and a second identified in the other two cases, as well as in a healthy contact who carried the virus but showed no symptoms.

"It was in the zone where vaccination activities are low because of the activities from armed groups and other groups," said Eugene Kabambi, WHO spokesman in the DRC. "Accessibility is very hard as most of the people are in the forest. To reach the hospital is very hard for them."

Vaccination campaigns planned

An emergency response is due to start next week to halt the outbreaks and ensure no more children are affected, Rosenbauer said. The WHO plans to actively search for cases, increase testing, and launch immunization campaigns targeting 750,000 at-risk children in affected areas.

A second vaccination campaign is set for July.

Polio is a highly infectious virus that affects the nervous system of young children and can result in paralysis. It is transmitted from person to person, mainly through contact with infected feces.

There is no cure for the disease, but it can be prevented through immunization.

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More than $11 billion has been invested by the international community to eradicate the disease since the Global Polio Eradication Initiative was established in 1988, resulting in a 99 percent drop in cases.

Just 42 cases were reported globally in 2016, down from more than 350,000 in 1985.